1. Field of the Invention
This invention relates to synergistic combinations of fungicides which, when applied to wood, give a synergistic result in providing improved resistance to mold, mildew and fungal decay. Wood treated with this combination, and a method of treating wood, are also included in the present invention.
2. Description of the Prior Art
Wood is one of the best structural materials for the construction of buildings because of its strength, ease of processing and relatively low cost. However, wood and wood-based materials, including cellulosic composites and plastic-wood composites, are susceptible to attack from various fungal organisms. Fungal attack can result in cosmetic damage (stain, mold and mildew) and/or structural degradation (decay) to both solid wood and wood-based composites.
Mold organisms, in addition to marring the appearance of wood, can present a health hazard in indoor environments since certain mold spores have the potential to be human respiratory allergens.
Sapstain is a particular problem for freshly sawn green lumber. Although attack by sapstain fungi does not generally result in the reduction of strength properties, sapstain can seriously degrade the value of lumber by impairing its appearance.
Preservative chemicals have been used since antiquity to prevent the onset of mold, stain and decay to wood in service. In recent times, the use of some wood preserving chemicals has been restricted or curtailed due to concerns about their safety to humans and their effects on the environment. Cost effectiveness of preservative treatments is also a major consideration since wood ultimately competes with non-cellulosic construction materials including steel, plastic and concrete.
Currently, a variety of fungicides are available to protect wood and wood composites from fungal attack. For example, it is known to use zinc borate to protect cellulosic composites, including particleboard, hardboard and oriented strand board, from fungal decay, as described in U.S. Pat. Nos. 4,879,083; 5,763,338; and 5,972,266. However, like most borates, zinc borate is not particularly effective against mold fungi. Recent work by Kop-Coat, Inc. (U.S. Pat. No. 6,416,789) has shown that combinations of IPBC, amine oxides and borates have a synergistic effect against many types of fungus in panel products such as OSB and hardboard.
Beginning in the 1930s, the sodium salt of pentachlorophenol (PCP) was the chemical of choice in preventing sapstain discoloration in freshly sawn lumber. By the mid-1980s, PCP was restricted for this use due to concerns over safety and environmental impact. This led to the development of a number of substitutes based on preservatives such as TCMTB, IPBC and DDAC. One of the leading antisapstain formulas continues to be NP-1®, a synergistic mixture of IPBC and DDAC (U.S. Pat. No. 4,950,685). New formulas have been developed in recent years. The performance of many of these has been evaluated by Oregon State University. (See Forest Products Journal Vol. 52, No. 2, pp 53-61 for a review of recent formulas.)
Since the 1940s, the main products for pressure treating have been creosote, PCP in fuel oil and CCA. In February 2002, the U.S. EPA restricted the use of CCA in residential applications of pressure treated wood, effective Dec. 31, 2003. Alternative treatments include borates, copper azole and ACQ.
Millwork treatment is a non-pressure application of preservatives to protect against mildew and decay. Solid lumber or wood composites are generally dipped in millwork treating solutions which also contain water repellents. WDMA Standard I.S. 4-2000 covers the preservative treatment of millwork components. Products approved under WDMA Hallmark Certification Program are based on TBTO, IPBC, TCMTB, propiconazole and tebuconazole. Synergistic anti-fungal combinations of propiconazole and tebuconazole are the subject of U.S. Pat. No. 5,223,524.
In recent years, there have been increasing concerns about mold growth in indoor residential environments. Mold can be a respiratory allergen to some individuals and is suspected of being a toxin in extreme exposure situations, although evidence of toxicity to humans is in question. Manufacturers of panel products such as OSB are taking steps to reduce or eliminate the possibility of mold growth on their materials. Potlatch Corporation has introduced OX-Terminator, a wood preservative treated panel product. See, e.g., International Application Publication No. WO 01/79339 A1. The active ingredient is based on a copper ammonium complex.
It is also known to use iodopropargyl derivatives such as 3-iodo-2-propynyl-n-butyl carbamate (IPBC) for protection against fungi which cause structural and cosmetic damage to wood. However, while effective, this compound used alone is expensive and requires larger amounts to achieve the desired end result.
U.S. Pat. No. 5,389,300 provides a composition for protecting sawn timber against wood discoloring fungi, containing a phenol fungicide and a halopropynyl fungicide such as IPBC. Other fungicides, insecticides, or active ingredients, including boron compounds, can be added to the composition.
U.S. Pat. No. 5,846,305 discloses a wood preservative composition comprising a copper compound, an amine solvent and a boron compound. The preferred boron compound is sold by U.S. Borax, Inc. under the tradename “TIM-BOR.”
U.S. Pat. No. Re36,798 provides a preservative composition for treatment of wood and other cellulosic materials, comprising a biocidal metal compound and a fungicidal compound containing a triazole group. Compositions of this invention may contain other organic fungicides, insecticides, or bactericides, including boron in any form, such as boric acid, boron, or boron esters.
U.S. Pat. No. 4,950,685 relates to a wood preservative composition which provides stain resistance to wood. The composition comprises a synergistic combination of a quaternary ammonium compound and IPBC.
U.S. Pat. No. 5,990,043 relates to an anti-fouling composition which includes a carrier, a binder, and an effective amount of at least one insecticide, which can be a carbamate. Synergistic effects are observed when combinations of two or more of the numerous insecticides listed are used in combination.
It is desired, therefore, to develop a wood treatment substance capable of protecting wood against fungal decay, mold and mildew in an economical, safe and environmentally responsible manner.